1. Field of the Invention
The present invention relates to a square filler for water treatment used mainly as a contact medium for aerobic or anaerobic treatment of sewage and to an apparatus for manufacturing such fillers.
2. Description of the Prior Art
Indispensable requirements for the filler as a contact medium for aerobic or anaerobic treatment of sewage performed in the vessel for sewage treatment are as follows:
(I) When viewed from the biological standpoint, it is desirable that such conditions as permitting the cycle of the food chain in the widest possible range continue in a limited water area and, at the same time, adapting coexistence of bacteria, protozoans, multicellular small animals, arthropods, mollusks, and vertebrates such as small fishes, as well as cleaning of treated water on a higher level (for example, treatment by denitrification and dephosphorylation) utilizing not only phytoplanktons but also duckweeds and various kinds of land grass or hydroponics of useful vegetables, to be prospective.
(II) Requirements from the user side are such that performance of water treatment is remarkably excellent and invariably stable, thereby enabling use of a small and inexpensive treating apparatus.
(III) The filler is light in weight and easy to handle, not requiring work but is used by simply being thrown into the vessel regardless of the shape and depth of the vessel.
(IV) The filler is preferably made of a chemically stable material and durable to permanent use in water.
(V) Fillers should possess an apparent specific gravity not different from that of water physically and geometrically, should neither sink nor float too high, should interwine with each other but not collect into one body, and are capable of suspending in water separately from each other.
(VI) Fillers must not induce an obstruction (clogging), caused by accumulated remains of dead organisms, to water flow passing through bodies thereof, must not confine bubbles therein, and must not rise beyond the water level.
Further, fillers are required to easily regain their initial state even if put under such unfavorable circumstances as above due to overload.